Positioning device and a hermetically sealed package formed therefrom

ABSTRACT

A hermetically sealed package (20) for an optical device (7) has a wall (21) which is formed partly by a positioning device (1) soldered to the wall (21). The positioning device (1) allows a fibre (4) to be aligned with the optical device (7) on either side of a transmissive window (3).

FIELD OF THE INVENTION

This invention relates to a positioning device for positioning one ormore optical devices relative to a transmissive window.

BACKGROUND OF THE INVENTION

It necessary for many semi-conductor devices to be packaged in ahermetically sealed environment, and so any connections into the packageneed to pass through a hermetically sealed feed-through. Optical fibresmay be used where it is necessary to conduct light to or from a package,in which case the fibre needs to be close to the device and has to passthrough the package wall. The fibre itself needs to be sealed to thefeed-through because otherwise there is a leakage path along the fibrebetween the fibre and the usual protecting sheath. Sealing the fibre tothe feed-through presents problems; firstly the fibre is delicate andcan be damaged by the handling processes of stripping, metalising andsoldering that are typical in the preparation of feed-through, and then,once the protecting sheath is removed the fibre may be subject to stressunless the sheath is also secured to the feed-through to maintaincontinuity of strength and covering for the fibre.

A known method of overcoming these problems is to incorporate atransmissive window with the package device arranged to transmit orreceive light through it but this has been found to cause difficulty inaligning the internal and external devices.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device whichlargely overcomes the alignment problems.

According to a first aspect of the present invention there is provided apositioning device comprising a single crystal and having a transmissivewindow portion having first and second sides oppositely disposed, whichis transparent to predetermined wavelengths, and a first locatingportion for locating a first optical device in a fixed position relativeto the first side of the window portion.

By forming the positioning device from a single crystal, the locatingportion and the window portion are in a fixed position relative to oneanother. The first optical device is therefore also located in a fixedposition relative to the window portion.

Preferably, there is a second locating portion for locating a secondoptical device in a fixed position relative to the second side of thewindow portion.

Two optical devices may thus be located in a fixed position relative tothe window portion, and also relative to one another.

The window may subsequently be made into a package such that the firstoptical device is external to the package, and the second optical deviceis internal to the package.

This reduces the problems of aligning the first optical device with thewindow portion and alignment with the second optical device within apackage can be obtained by accurate fixing of the positioning device tothe package.

Conveniently, the first optical device is an optical fibre, and thesecond optical device is a semi-conductor device.

The window portion is transparent to wavelengths corresponding to thewavelength response or emission wavelength of the semi-conductor device.The fibre and semi-conductor device may thus be located relative to thewindow and to one another such that light emitted from thesemi-conductor device passes through the window and is coupled to thefibre. Alternatively, light may be emitted from the fibre, pass throughthe window and be incident on the semi-conductor device.

Where the first optical device is an optical fibre the window portionmay conveniently be formed by a thin region at the end of the bore inthe single crystal block, the walls of the bore forming the firstlocating portion. The diameter of the bore is such that the fibre may bepush-fitted into it. Once inside the bore, the bore acts as a supportfor the fibre.

Alternatively, the first locating portion may be in the form of aV-groove in the single crystal block. The groove may be formed by usingchemical etching processes, for example.

The device to be sealed in a package is generally mounted on a planarsurface. The second locating portion may therefore be in a form ofledge. The second optical device may then be placed on the ledge to belocated relative to the window and so also to the first optical deviceexternal the package.

The positioning device may have a second window portion spaced apartfrom the first window portion, the second locating portion forconnecting the first and second window portions and for supporting thesecond optical device there between and for locating the second opticaldevice in a fixed position relative to the first and second windowportion.

Preferably, the first and second windows form opposite sides of acavity. The second optical device is thus located in the cavity whichmay be sealed to form a package simply by adding further single block toform a top for the cavity. When the device is incorporated into apackage the first, second and third optical devices are all aligned.

Conveniently, the third optical device is an optical fibre, and thesecond optical device is an optical amplifier. It is thus possible toalign two optical fibres and an optical amplifier such that light may beemitted from the first optical fibre such that it passes through thefirst window and is incident upon the optical amplifier. The opticalamplifier will then emit light which passes through the second windowand is incident upon the second optical fibre.

According to a second aspect of the present invention, there is provideda positioning device according to the first aspect of the inventionhaving means which form a hermetically sealed package enclosing thesecond optical device, wherein the or each window forms part of the saidpackage.

The positioning device may be manufactured remote from the package, andthe first and second optical devices may be aligned relative the windowand to one another prior to manufacture of a package according to thesecond aspect of the invention. The positioning device with the firstand second optical devices may then be incorporated into a package.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to the accompanying drawings in which:

FIG. 1 is a sectional view through a positioning device according to theinvention suitable for locating an optical device with respect to awindow portion;

FIG. 2 is a cross section of the device of FIG. 1 along the axis II--II;

FIG. 3 is a sectional view of a positioning device according to theinvention suitable for locating a first and a second optical device withrespect to the window portion;

FIG. 4 is a cross section of the device of FIG. 3 along the axis IV--IV;

FIG. 5 is sectional view of a positioning device according to theinvention suitable for locating three optical devices with respect totwo window portions;

FIG. 6 is a cross section of the device shown in FIG. 5 along the axisVI--VI;

FIG. 7 is a sectional view of a device package incorporating thepositioning device of FIG. 3 and 4.

DETAILED DESCRIPTION OF A PRESENTLY PREFERRED EXEMPLARY EMBODIMENT

Referring to FIG. 1, a positioning device 1 is formed from a singlecrystal of silicon. The positioning device is in the form of a bore, theend 2 of which forms a transmissive window 3. The thickness of thewindow is about 10 to 30 microns. The remainder of the bore acts as asupport for an optical fibre 4 which is positioned within the bore. Whenin position, the fibre 4 is located in a fixed position relative to thewindow 3. The cross sectional formation of the device one is shown inFIG. 2. The diameter of the bore is arranged to be slightly larger thanthe diameter of the fibre, in order that the fibre just fits inside thebore, and is held in the desired location.

Referring now to FIGS. 3 and 4, a second embodiment of the invention isillustrated. A positioning device 1 formed from a single crystal ofsilicon comprises a fibre receiving support 5, which is in the form of aV-groove. The V-groove 5 is adapted to receive a fibre 4 such that thefibre is located in a fixed position relative to the window 3. Inaddition, the positioning device 1 has a ledge 6 formed integrally withthe rest of the device. The ledge 6 is adapted to support an opticaldevice 7 such that the device 7 is located in fixed position relativethe window 3. The device 7 may be a light emitting device such a laserchip. The positioning device 1 is shaped such that the optical axis ofthe device 7 is coaxial with the optical axis of the fibre 4. The window3 is transparent to wavelengths corresponding to emission wavelengths ofthe device 7. Light emitted by the device 7 is transmitted through thewindow 3 to the fibre 4. A separate silicon block 8 formed into aV-groove of similar dimensions to that of the V-groove 5 may be placedon top of the fibre 4 in order to hold it more securely in place. Thecross sectional configuration of the device is shown in FIG. 4. The endof the fibre 4 is preferably lensed and anti reflection coated andlocated close to the window 3 so that the spacing from the fibre end tothe device 7 is less than about 50 microns, and in order to reduceattenuation the window is coated with an anti reflection coating.

Referring to FIGS. 5 and 6 a third embodiment of the invention isillustrated. The positioning device 1 comprises a first fibre receivingsupport 9 formed as V-groove, and which is adapted to locate a fibre 4in a fixed position relative to a window 3. The device further comprisesa second fibre receiving support 10 formed as V-groove adapted to locatea second fibre 11 in a fixed position relative to a second window 12.The positioning device 1 is shaped to form a cavity 13 comprising asupport 14 on which an optical device such as optical amplifier 15 maybe located in a fixed position relative to the windows 3 and 12. Theconfiguration of the positioning device 1 is such that the optical axisof the fibre 4, fibre 11, and optical amplifier 15 are coaxial. Afurther block 16 of silicon may be soldered to windows 3 and 13 in orderto form a hermetically sealed container inside which the opticalamplifier 15 is positioned. A heat sink 17 may be attached to thesupport 14 in order to dissipate any heat generated by the opticalamplifier.

Referring to FIG. 7, a device package is shown which incorporates thepositioning device of FIGS. 3 and 4. A device package 20 comprises apackage wall 21 a part of which is formed by the positioning device 1.The positioning device 1 is soldered at 22 and 23 to the package wall 21thus forming a hermetically sealed package 20. The optical device 7 isthus hermetically sealed.

Within the context of this specification "optical" refers to not onlythe visible region of the electromagnetic spectrum that also includesultra-violet and infra-red radiation, and especially include that parthaving a wavelength greater that 1.1 microns.

I claim:
 1. A positioning device comprising a single crystal:said singlecrystal having a transmissive window portion having first and secondsides oppositely disposed and transparent to predetermined wavelengths,said single crystal also having a first locating portion for locating afirst optical device in a fixed position relative to the first side ofthe window portion, and said single crystal further having a secondlocating portion for locating a second optical device in a fixedposition relative to the second side of the window portion.
 2. A deviceaccording to claim 1 wherein: said single crystal also has a secondwindow portion spaced apart from the first window portion,the secondlocating portion connecting the first and second window portions and forsupporting the second optical device therebetween and for locating thesecond optical device in a fixed position relative to the first andsecond window portions.
 3. A device according to claim 2 wherein:saidsingle crystal includes a third locating portion disposed on theopposite side of the second window portion with respect to the secondlocating means for locating a third optical device.
 4. A deviceaccording to claim 1, 2 or 3 including as the first optical device anoptical fibre.
 5. A device according to claim 3 including as the firstand third optical device respective 1 optical fibers.
 6. A deviceaccording to claim 1, 2 or 3 wherein the or each window portion istransparent to wavelengths corresponding to the wavelength response oremission wavelengths of the second optical device.
 7. A device accordingto claim 5, wherein the first window portion is formed by a thin regionat the end of a bore in a single crystal block, the bore forming thefirst locating portion by being adapted to receive a fibre.
 8. A deviceaccording to claim 5 wherein each window portion is formed by a thinregion at the end of a bore in a single crystal block, the bores formingthe first and third locating portions respectively by being adapted toreceive a fibre.
 9. A device according to any one of the precedingclaims 1, 2 or 3 wherein the first locating portion is in the form of aV-groove.
 10. A device according to claim 5 wherein the first and thirdlocating portions are each in the form of a V-groove.
 11. A deviceaccording to any one of claims 1, 2 or 3 wherein the second locatingportion is in the form of a ledge.
 12. A device according to any one ofclaims 1, 2 or 3 wherein the second optical device is a laser chip. 13.A device according to any one of the preceding claims 1, 2 or 3comprising means which form a hermetically sealed package enclosing thesecond optical device, wherein the or each window forms part of the saidpackage.
 14. A single crystal formed to include:an opticallytransmissive window, a positioning structure for positively locating anoptical fibre end with respect to a predetermined location on a firstside of said window, a further positioning structure for locating anoptical signal processing device with respect to a second side of saidwindow, a second optically transmissive window disposed adjacent saidfurther positioning structure and opposite said first window, and athird positioning structure disposed adjacent said second opticallytransmissive window for locating a further optical fiber end withrespect to said second window.
 15. A single crystal as in claim 14hermetically sealed to an aperture in a wall of a package housing anoptical signal processing device.